It is known to join two pipes together end-to-end by forming a joint between a circumferentially adjustable annular band and the ends of the two pipes. Typically, the annular band used in these joints has two end edges and two annular side edges. When the band is circumferentially adjusted, the two end edges move relative to one another. Such joints have been sealed by trapping an elastomeric gasket between an outside surface of the two pipe ends and an inside surface of the annular band.
These joints have been used to join annularly grooved ends of corrugated pipe in storm sewer systems. The annular band typically used with such corrugated pipe has a generally flat inside surface between two annular ribs, one rib running alongside each side edge. These two annular ribs are spaced far enough apart to mate with one annular groove on each pipe end to help prevent the resulting joint from being pulled apart. The joints in storm sewer systems are generally expected to withstand water pressures up to a maximum of about 15 psi with only minimal leakage allowed. Two types of gaskets have been used to seal the joints of such systems, O-ring gaskets and flat gaskets. A typical O-ring gasket has a continuous O-shape, with a circular cross-section. A typical flat gasket has a flat top and bottom surface that are generally parallel and two side edges, giving the gasket a generally rectangular cross section.
When O-ring gaskets are used to seal such storm sewer pipe joints, at least two gaskets are used, with each gasket being seated in one of the annular grooves on each pipe end. When the joint is formed, each O-ring gasket is positioned between its respective annular groove and a portion of the flat inside surface of the band. One advantage of using O-ring gaskets is that they can be pre-positioned on the pipe end before the joint is assembled in the field. However, one drawback is that the O-ring gaskets, by themselves, do not provide a complete seal for the joint. Reducing the circumference of the annular band compresses each O-ring gasket between only a trough portion of its respective annular groove and a portion of the inside flat surface of the annular band. Additional steps must be taken to separately seal the two end edges of the annular band when O-ring gaskets are used. This can be accomplished by applying a sealant between the two end edges.
Unlike the O-ring gaskets, the single piece flat gasket is used, when the flat gasket is used, the flat gasket forms a seal in the joint by being circumferentially extended completely around both of the pipe ends, with the side edges of the gasket extending out beyond at least a portion of the annular grooves on each pipe end which mate with the two annular ribs on the band. Thus, no separate steps are required to seal the end edges of the annular band. A portion of the gasket along each side edge is sandwiched between one of the annular band ribs and its mating annular pipe groove. The balance of the bottom surface of the flat gasket between the two band ribs usually only contacts upper or crest portions between adjacent annular grooves of each pipe end.
While O-ring and flat gaskets are commonly used for such pipe joints, they do not consistently provide the seal integrity (i.e. tightness) desirable for such pipe joints. Pipe joints formed with these gaskets are known to leak. Therefore, there is a need to provide a gasket which more reliably seals such pipe joints or at least allows only minimal leakage.